Composite laminate automotive structures

ABSTRACT

A laminate support beam includes an outer structural member which has a channel shape with a longitudinal rigid inner member precoated with structural foam to form a drop-in insert unit which is dropped into the channel of the outer structural member when the structural foam is heat expandable to intimately bond to the inner surface of the outer member and provide a lightweight reinforcement for the outer member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of application Ser. No.08/751,093 filed Nov. 15, 1996, now U.S. Pat. No. 5,884,960 which inturn is a continuation in part of application Ser. No. 08/245,798 filedMay 19, 1994, now U.S. Pat. No. 5,575,526.

TECHNICAL FIELD

The present invention relates generally to automotive body structuralmembers and, more specifically, relates to techniques for increasingstrength and stiffness of automotive body structural members.

BACKGROUND OF THE INVENTION

In a number of applications, particularly in the automotive industry, itis important to provide high-strength structural members at the lowestpossible mass. A number of composite materials have been proposed byothers in the past for use in forming structural members, includingexotic light weight alloys. In the automotive industry, however, theneed for mass reduction without sacrificing strength must be balancedagainst the cost of the product to the consumer. Thus, there is a needfor maintaining or increasing the strength of structural members such asrockers, windshield, pillars, radiator support beams, drive shafts, sideimpact beams, and bumpers without significantly increasing materials andlabor costs.

The reinforcement of motor vehicle structural members through the use ofcomposite materials is known. For example, the present inventor hasdisclosed a number of metal/plastic composite structures for use inreinforcing motor vehicles components. In U.S. Pat. No. 4,901,500,entitled “Lightweight Composite Beam”, a reinforcing beam for a vehicledoor is disclosed which comprises an open channel-shaped metal memberhaving a longitudinal cavity which is filled with a thermoset orthermoplastic resin-based material. In U.S. Pat. No. 4,908,930 entitled,“Method of Making a Torsion Bar,” a hollow torsion bar reinforced by amixture of resin with filler is described. The tube is cut to length andcharged with a resin-based material.

In U.S. Pat. No. 4,751,249, entitled, “Reinforcement Insert for aStructural Member with Method of Making and Using the Same”, a precastreinforcement insert for structural members is provided which is formedof a plurality of pellets containing a thermoset resin with a blowingagent. The precast is expanded and cured in place in the structuralmember. In U.S. Pat. No. 4,978,562, entitled, “Composite Tubular DoorBeam Reinforced with a Syntactic Foam Core Localized at the Mid Span ofthe Tube”, a composite door beam is described which has a resin-basedcore that occupies not more than one-third of the bore of a metal tube.

In addition to the present inventor's own prior work, a number of metallaminates constructions are known in which flat metal plates are bondedtogether by an intervening layer of resin. It is also known to form ametal laminate sheet for use as a floor panel member which comprises apair of flat metal sheets having an intervening layer of asphalt orelastic polymer.

Although filling sections with plastic foam does significantly increasesection stiffness (at least when high-density foams are utilized), theyalso increase mass and thus part weight, which, as stated, is anundesirable feature in automotive applications. Moreover, althoughincreasing the metal gauge of a section or adding localized metalreinforcements will increase stiffness, as the metal thicknessincreases, it is more difficult to form the part due to limitations inmetal forming machines. Importantly, in many applications increasingmetal gauge will not work effectively because stiffness frequency isproportional to section stiffness divided by section mass: f≈{squareroot over (K/m)} (i.e., frequency is proportional to the square root ofstiffness over mass). Mass and stiffness are increased proportionately,with no resultant change in the dynamic stiffness frequency of the part.

In addition, filling a section entirely with foam creates a large heatsink and requires elaborate sealing operations to close access holes inthe stampings. Also, the presence of the foam may interfere with theplacement of interior trim panels, wiring harnesses, and hinges.

Accordingly, it would be desirable to provide a low-cost technique forincreasing the stiffness of a section without proportionately increasingthe mass. The present invention provides sections which have increasedstiffness values with no significant increase in mass and without theuse of high volumes of expensive resins. In many applications, thepresent invention reduces vibrations which cause unwanted “shake” of acomponent.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a hollow laminate beamcharacterized by its high-stiffness-to-mass ratio. The beam has an outerportion which is separated from an inner tube by a thin layer ofstructural foam. The cavity defined by the beam may be open or closedalong its length.

In another aspect, the hollow laminate beam of the present invention isan automotive radiator support beam having an outer metal section and agenerally rectangular inner tube, which may be open on one side. Atleast three sides of the rectangular inner tube are coated with astructural foam which is disposed between the rectangular inner tube andthe outer metal section and in contact therewith. A metal cap is weldedin place to complete the beam and retain the inner tube. The diameter ofany through holes in the inner tube which are in alignment withthrough-holes in the outer portion are larger than the outer portionthrough-holes such that the structural foam does not block thethrough-hole clearances of either metal thicknesses.

In still another aspect, the laminate beam of the present invention isan automotive windshield pillar. A hollow metal tube is disposed withinthe pillar and is separated from the outer pillar stampings by a thinlayer of structural foam.

In still another aspect, the laminate beam of the present invention isan automotive rocker panel assembly. The rocker panel assembly comprisesmating inner and outer panel sections which form a generally rectangularrocker panel wall structure. Positioned within the rocker panel wallstructure is a closely fitting inner metal tube which defines a cavity.A thin layer of structural foam is disposed between the rocker panelwall structure and the inner tube structure.

In still another aspect the beam is a motor vehicle drive shaft. Aninner tube is closely received within the outer drive shaft housing,thereby defining an annulus. A layer of foam is disposed in the annulus.

The present invention also provides a method of increasing thestiffness-to-mass ratio of a beam, wherein the beam defines a cavity.The method includes the steps of forming a tube which fits within thecavity defined by the beam; placing a layer of resin on at least aportion of the outer surface of the tube; and inserting the tube in thecavity, with the resin contacting the inner wall of the tube.

In still another aspect, the present invention comprises a C-railsection for use in truck frames. An inner stamped or rolled C-shapedmember is separated from the outer C-frame rail by a layer ofresin-based material.

In still another aspect, a plurality of plugs made of a foam whichdisintegrates at high temperatures are used to close through-holes in apart which is subsequently filled with a core material. The part is thenpassed through an oven which melts or disintegrates the plugs.

In still another aspect, the present invention provides a door beam orside impact beam for a motor vehicle door which provides increasedcompression resistance at minimal cost and weight. A local reinforcementis provided in the midspan of a steel shell. The local reinforcementincludes a high-strength, thin steel stamping and a layer of thermallyexpandable foam. This allows the outer shell to be formed of relativelyinexpensive mild steel. The foam is sandwiched between the outer shelland the thin steel stamping.

In one aspect, the outer steel shell and inner steel stamping havingmating flanges that are welded together by spot welds.

In still another aspect, a reinforced bumper is provided for a motorvehicle. A local reinforcement provides a steel-foam-steel laminatehigh-strength structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the front end of a motor vehicle, withthe engine removed and the body shown in phantom.

FIG. 2 is an exploded perspective view of a radiator support beam madein accordance with the present invention.

FIG. 3 is a plan view of the radiator support beam of FIG. 2.

FIG. 4 is a front elevational view of the radiator support beam of theradiator support beam of FIG. 2.

FIG. 5 is a fragmentary longitudinal cross section along lines 5—5 ofFIG. 3.

FIG. 6 is a cross section along lines 6—6 of FIG. 3.

FIG. 7 is a plan view of another radiator support beam made inaccordance with the present invention in another configuration.

FIG. 8 is a fragmentary longitudinal cross section taken along lines 8—8of FIG. 7.

FIG. 9 is a cross section along lines 9—9 of FIG. 7.

FIG. 10 is a cross section of a rocker panel made in accordance with thepresent invention.

FIG. 11 is a cross section of a windshield pillar made in accordancewith the present invention.

FIG. 12 is a cross section of a drive shaft made in accordance with thepresent invention.

FIG. 13 is a cross section of a C-rail section made in accordance withthe present invention.

FIG. 14 is a cross section of a radiator support beam made according toanother aspect of the present invention.

FIG. 15 is a perspective view of a reinforced door beam in accordancewith the present invention.

FIG. 16 is a section along lines 16—16 of FIG. 15.

FIG. 17 is a section along lines 17—17 of FIG. 15.

FIG. 18 is a cross section of a reinforced door beam in anotherconfiguration.

FIG. 19 is a perspective view of a reinforced door beam in accordancewith the present invention.

FIG. 20 is a section along lines 20—20 of FIG. 19.

FIG. 21 is a fragmentary perspective view of one end of the beam shownin FIG. 19.

FIG. 22 is a perspective view of a reinforced bumper made in accordancewith the present invention.

FIG. 23 is a cross section along lines 23—23 of FIG. 22.

FIG. 24 is a fragmental view of the oversized through-holes of thepresent invention shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 of the drawings, a motor vehicle 10 is shownwith the engine removed and the body illustrated in phantom. Radiatorsupport structure or beam 12 is mounted on the chassis and serves tosupport the vehicle radiator (not shown). In FIG. 2, radiator supportbeam 12 is illustrated in exploded view having outer shell or portion 14which in this embodiment is a steel stamping. An inner tube, here shownas channel-shaped tube 16, is provided having a layer of resin-basedmaterial 18 applied to selected surfaces. Cap 20 is seen having aplurality of through-holes 22 and serves to enclose channel-shaped tube16 within outer shell 14.

More specifically, and referring now of FIGS. 2 through and 6 and 24,outer shell 14 defines a cavity or channel 24. A number of through-holes26 are seen through which electric wiring (not shown) may extend. Outershell 14 includes a laterally extending mounting bracket or plateportion 28 which is secured to components of the engine assembly.

The benefits of the present invention are provided by inner tube orinner portion 16 which in this case is roll-formed metal, for examplethin gauge steel, which is formed so that it may be closely fittedwithin cavity 24 of outer shell 14. Inner tube 16 in this embodimentclosely conforms to the geometry of outer shell 14, including having alateral plate 30 that mates with mounting bracket 28. By providing alayer of resin-based material 18 on selected surfaces of inner tube 16and then assembling inner tube 16 and outer shell 14 to form thetube-in-tube construction shown best in the cross section of FIG. 6, thestiffness of beam 12 is increased significantly without a significantincrease in mass. Accordingly, as shown in FIGS. 2 and 6, a layer of aresin-based material 18 is applied, shown here on three sides of innertube 16.

A number of resin-based compositions can be utilized to form resin-basedlayer 18 in the present inventions. The preferred compositions impartexcellent strength and stiffness characteristics to beam 12 while addingonly marginally to the weight. With specific reference now to thecomposition of the resin-based layer, the density of the material shouldpreferably be from about 15 pounds per cubic feet to about 40 pounds percubic feet to minimize weight. The melting point of resin-based layer18, heat distortion temperature, and the temperature at which chemicalbreakdown occurs must also be sufficiently high such that layer 18substantially maintains its structure at high temperatures typicallyencountered in paint ovens and the like. Therefore, resin-based layer 18should be able to withstand temperatures in excess of 300 degrees F. andpreferably 350 degrees F. for short times. Also, the resin-based layer18 should be able to withstand heats of about 180 degrees F. to 220degrees F. for extended periods without exhibiting substantialheat-induced distortion or degradation.

In more detail, resin-based layer 18 includes a synthetic resin, acell-forming agent, and a filler. A synthetic resin comprises from about35.0 percent to about 95.0 percent by weight, preferably from about 75.0percent to about 94.0 percent by weight, and most preferably from about78.0 percent to about 90.0 percent by weight of layer 18. As usedherein, the term “cell-forming agent” refers generally to agents whichproduce bubbles, pores, or cavities in layer 18. That is, resin-basedlayer 18 has a cellular structure, having numerous cells disposedthroughout its mass. This cellular structure provides a low-density,high-strength material, which, in beam 12, provides a strong, yetlightweight structure. Cell-forming agents which are compatible with thepresent invention include reinforcing “hollow” microspheres ormicrobubbles which may be formed of either glass or plastic. Plasticmicrospheres may be either thermosetting or thermoplastic and eitherexpanded or unexpanded. In one embodiment, unexpanded microspheres areused which are then expanded to form resin-based layer 18. The preferredmicrospheres are from about 1.0 to about 250 and preferably from about10 to about 180 microns in diameter. The cell-forming agent may alsocomprise a larger, lightweight material such as macrospheres of greaterthan 400 microns in diameter. Also, the cell-forming agent may comprisea blowing agent which may be either a chemical blowing agent or aphysical blowing agent. Glass microspheres are particularly preferred.Where the cell-forming agent comprises microspheres or macrospheres, itconstitutes from about 1.0 percent to about 60.0 percent by weight,preferably from about 1.0 percent to about 35.0 percent by weight, andmost preferably from about 3.0 percent to about 20.0 percent by weightof layer 18. Where the cell-forming agent comprises a blowing agent, itconstitutes from about 1.0 percent to about 10.0 percent by weight,preferably from about 1.0 percent to about 5.0 percent by weight, andmost preferably from about 3.0 percent to about 5.0 percent by weight oflayer 18. Suitable fillers include glass or plastic microspheres, silicafume, calcium carbonate, milled glass fiber, and chopped glass strand.Glass microspheres are particularly preferred. Other materials may besuitable. A filler comprises from about 1.0 percent to about 55.0percent by weight, preferably from about 5.0 percent to about 24.0percent by weight and most preferably from about 7.0 percent to about19.0 percent by weight of resin-based layer 18.

Preferred synthetic resins for use in the present invention includethermosets such as epoxy resins, vinyl ester resins, thermoset polyesterresins, and urethane resins. It is not intended that the scope of thepresent invention be limited by molecular weight of the resin. Where theresin component of the liquid filler material is a thermoset resin,various accelerators, such as “EMI-24” (imidazole accelerator) and“DMP-30”. and curing agents, preferably organic peroxides such as “MEK”peroxide and “Percadox”, may also be included to enhance the cure rate.A functional amount of accelerator is typically from about 0.1 percentto about 4.0 percent of the resin weight with corresponding reduction inone of the three components, resin, cell-forming agent or filler.Similarly, the amount of curing agent used is typically from about 12percent to about 4 percent of the resin weight with a correspondingreduction in one of the three components, resin, cell-forming agent orfiller. Effective amounts of processing aids, stabilizers, colorants, UVabsorbers and the like may also be included in layer. Thermoplastics mayalso be suitable.

In the following tables, preferred formulations for resin-based layer 18are set forth. It has been found that these formulations provide a layer18 which results in a beam 12 having a stiffness-to-mass ratio ofgreater than 1, where 1 is a normalized stiffness-to-mass ratio of ahollow or open C-channel metal beam regardless of mass.

Formulas I and III are preferred for use with clean metal surfaces(i.e., after removing any residue on the contacting metal surfaces suchas mill oils and drying compounds). Formula II does not requireextensive precleaning of the metal.

PERCENTAGE INGREDIENT BY WEIGHT FORMULA I Polyester Resin 80.9(“ARS-137-69”) “Percadox 16N” 1.1 “3M C15” 18 FORMULA II EPON 828 54.5Haloxy 62 7.5 Der 732 6.1 Expancel 551DU 2.0 SG Micros 8.8 3M K20 17.7DI-CY 3.4 FORMULA III Polyester Resin 48.8 (“ARISTECH 13031”) “Percadox16N” 0.7 “SG Micros” (PA IND) 50.5

As will be appreciated by those skilled in the art, EPON 828 is an epoxyresin, Haloxy 62 is an epoxy diluent, Der 732 is a flexible epoxy,Expancel 551 DU is a blowing agent, SG Micron and 3M K20 aremicrospheres, and DI-CY is a curing agent.

A number of methods of applying layer 18 to reinforcement tube 16 may besuitable, for example by spraying the resin-based material onto thesurface of tube 16. It may be suitable to fill the space between theinner and outer tubes after they are assembled. Most preferred is theapplication of the resin-based material using a duck-bill applicatorwhich applies a wide, even ribbon of resin on the surfaces of tube 16.In most applications, the thickness (inches) of layer 18 should be fromabout 0.060 to about 0.50 and more preferably from about 0.10 to about0.25, where the preferred foam compositions described herein areutilized.

In those embodiments of the present invention in which outer shell 14has one or more through-holes 26, for example, for the passage ofelectrical wiring or the like, it will be necessary to provide matchingthrough-holes 32 in inner tube 16 in register with the through-holes 26of the outer shell. Since structural foam layer 18 could in someinstances block all or a portion of through-holes 32, requiring aseparate assembly step of clearing the foam material from the hole, In apreferred embodiment of this invention, clearance is obtained bycreating oversized through-holes 32 in alignment with through-holes 26.It is preferred that the diameter of through-holes 32 be at least 20percent larger than that of through-holes 26, but in some applicationsequal size through-holes will be sufficient. In this manner, resin orfoam which extends from the edges of inner tube 16 into the clearance ofthrough-holes 32 will generally not block wire, clips, or screws and thelike that are threaded through through-holes 26. This concept is alsoillustrated in FIG. 24 (as viewed looking through hole 32 from theinside) in which a portion of layer 18 extends into the clearance ofthrough-hole 32 during application, but not to the margins ofthrough-hole 26. In the event that layer 18 does obstruct any of thethrough-holes 32, it may be blown clear using an air jet before layer 18solidifies.

Referring again to FIGS. 2 and 5, cap 20 closes radiator support beam 12as well as cavity or channel 34 defined by inner tube 16. Cavity 34 willgenerally be clear (i.e., inner tube 16 will be hollow) other than forthe presence of wiring. Cap 20 is preferably welded in place. Theeffective thickness of the reinforced walls of beam 12 is typically fourto five times that of shell 14, with very little increase in weight.

Where layer 18 is a thermoset and/or expandable resin-based material,layer 18 may be cured and/or expanded in place from the heat of theB-coat oven. It is preferred that layer 18 bond together shell 14 andtube 16. It should also be noted that the construction of the presentinvention allows the B-coat to drain, which would not be possible if theentire beam were foam-filled. In addition, the minimal amount of foamwhich is used does not create a heat sink body as is the case withlarge, dense foam areas and the minimal amount of foam usage reducesmaterials cost. Also, the need for plugs or the like to allow foamfilling of the entire beam is eliminated.

In another embodiment of the present invention, and referring now toFIGS. 7, 8, and 9, inner tube 16′ is shown which has a rectangular shapeand is in the nature of a closed rectangular tube (i.e., closed alongits length). As with channel-shaped inner tube 16, rectangular innertube 16′ will generally be hollow. Layer 18′ is shown applied to threesides of inner tube 16′. In general, at least about 25 percent and morepreferably at least about 75 percent of the mating area which forms thetube-in-tube region of the beam should be covered by layer 18′.

Where desired, inner tube 16′ at through-holes 32′ may be flangedinwardly toward outer shell 14′ such that the flange serves as a closureto confine and isolate layer 18′. Alternatively, outer shell 14′ atthrough-holes 26′ may be flanged inwardly toward inner tube 16′ for thesame purpose. Also, plugs or grommets in through-holes 26′ and/or 32′can be used for this purpose

A number of materials can be used to form the outer shell and the innertube such as plastic or metal, but steel is preferred. The outer shellmetal gauge (inches) will typically be from about 0.030 to about 0.090.The inner tube metal gauge will typically be from about 0.025 to about0.050.

A number of additional specific applications of the present inventionwill be apparent in light of the teachings herein. A few of thepreferred applications are set forth hereinafter.

Referring now to FIG. 10 of the drawings, metal automotive rocker panelassembly 40 is shown having metal rocker inner panel 42 and metal rockerouter panel 44. Inner tube 46 is provided along with a layer ofresin-based material 48 disposed thereon which separates inner tube 46from the rocker panels 42 and 44. An adhesive bead 45, which may be madeof the same material as layer 48, is provided adjacent trim holes 50.The assembly is welded at flanges 52.

In FIG. 11, the present invention is shown in use as a windshield pillar54. Again, the tube-in-tube construction is employed with windshieldpillar outer 56 being separated from windshield pillar inner tube 58 byresin-based layer 60. The assembly is welded together at flanges 62.

In FIG. 12, a cross section of automotive driveshaft 64 is shown havingan outer metal tube 66 separated from an inner metal tube 68 by a layerof structural foam 70.

In FIG. 13, C-rail 72 is shown having outer wall section 74 separatedfrom inner tube or channel portion 76 by a layer of structural foam 78.

In still another embodiment, and referring now to FIG. 14 of thedrawings, the entire cavity of a structural member such as radiatorsupport beam 80 having cap 81 and shell 83 is filled with a cementationsmaterial or a structural foam 82. In order to prevent material 82 fromflowing out of cavity 84 through through-holes 86 and 88, plugs 90 and92 are provided, preferably formed of a foam material such as STYROFOAM®(expanded polystyrene) which will disintegrate at temperatures presentin automotive treatment ovens. The plugs are preferably inserted intoall through-holes except those through which material 82 is injected. Inthis manner, plugs 88 and 90 are automatically “removed” so thatsufficient clearance is maintained for wiring clips and the like. Thepreferred material for use in forming material 82 is described in U.S.Pat. No. 5,124,186, “Composite Tubular Door Beam Reinforced with aReacted Core Localized at the Mid-Span of the Tube”, dated Jun. 23,1992, the entire disclosure of which is incorporated by reference. Mostpreferably, the material described beginning at line 41 of column 10 ofthe aforementioned U.S. Pat. No. 5,124,186 is preferred.

In still another embodiment, and referring now to FIGS. 15 and 16 of thedrawings, a reinforced door beam or side impact beam 100 is seen havingan outer structural shell 102 which is preferably formed of mild steel(preferably a yield strength of 25,000-35,000 psi) or non-heat treatedhigh-strength steel having a nominal thickness of from about 0.050 inchto about 0.100 inches. Structural shell 102 is reinforced locally inaccordance with the present invention to provide compression facereinforcement element 104 (shown in phantom in FIG. 15). In the mostpreferred embodiment, reinforcement 104 occupies less than about thecenter one-third of structural shell 102 but preferably more thanone-eighth of the length of structural shell 102.

Referring now also to FIG. 17 of the drawings, reinforcement 104 isshown in one embodiment as a three-sided reinforcement with a layer ofstructural foam 106 disposed along three inner surfaces 108, 109, and110 of structural shell 102. In the illustrated embodiment of FIGS. 15,16, and 17, foam layer 106 is shown spanning longitudinal gap 112 ofstructural shell 102, although this orientation is not required. Foamlayer 106 is preferably from about 0.050 to about 0.25 inches thick.Disposed on inner surfaces 108, 109, and 110 of foam layer 106 is innershell 114 which is preferably formed of thin ultra high-strength steel,preferably having a nominal thickness of from about 0.025 to about 0.080inches. Inner shell 114 is co-extensive with foam layer 106. That is,inner shell 114 has a size and geometry which matches foam layer 106.

In one mode of fabrication, reinforced door beam 100 is fabricated byextruding a ribbon or sheet of unexpanded resin-based material which isthen applied to the surface of inner shell 114 (preformed to the desiredgeometry). Inner shell 114 would thus serve the function of a carriermember for the unexpanded material that forms foam layer 106. Innershell 114 with the attached resin can then be inserted into one end ofstructural shell 102 and enough pressure applied to bond the resin inplace, i.e., to hold the unexpanded material that forms foam layer 106and its attached inner shell 114 in place in the mid portion of outershell 102. In addition, it may be desirable to add dimples (not shown)in outer shell 102 to hold inner shell 114 and its resin layer in place.

Reinforced door beam 100 is attached inside a door cavity in any numberof configurations such as that shown in U.S. Pat. No. 4,978,562mentioned above, the entire disclosure of which is incorporated hereinby reference. The precise attachment means such as end pieces and/orwelding is not a critical part of the present invention. Once installedin the vehicle door, reinforced door beam 100 is heated to a temperaturesufficient to thermally expand or “foam” layer 106, such as when themotor vehicle is placed in a paint oven or the like. At the blowingagent activation temperature, the resin that forms layer 106 expands toits final form and solidifies to form a strong bond between inner shell114 and outer shell 102. Since layer 106 is a structural foam and innershell 114 is a thin high-strength steel, structural shell 102 isreinforced with a minimum weight increase.

In FIG. 18 of the drawings, reinforced door beam 100′ is shown havingouter structural shell 102′, foam layer 108′ and inner shell 114′. Inthis embodiment, foam layer 108′ (and inner shell 114′) are four-sidedin contrast to the three-sided embodiment described in the previousembodiment. In both the three-sided embodiment and the four-sidedembodiment, the material used to form the thermally expandable foamlayer is that which was previously described in connection with theprevious embodiments.

In another embodiment, as shown in FIG. 19 reinforced door beam or sideimpact beam 150 is provided with outer shell 152, again a mild to mediumstrength steel having a thickness of 0.050 to 0.100 inch, which includeswide flanges 154 on one side thereof. Flanges 154 will typically have awidth of from about 0.43 to about 0.75 inches. Centrally disposed innershell 156 has matching flanges 158 and is formed of thin high-strengthsteel (nominal thickness of from about 0.025 to about 0.080 inches).Inner shell 156 occupies only about one-third of the length of outershell 152.

As best seen in FIGS. 20 and 21, inner shell 156 is separated from outershell 152 by a layer 160 of thermally expanded resin-based material. Asexpanded, layer 160 has a preferred thickness of from about 0.060 toabout 0.25 inches. In this embodiment, structural foam layer 160 doesnot reside between flanges 154 and flanges 158. Instead, flanges 154 andflanges 158 are spot-welded together. Thus, the invention provideslocalized reinforcement to force in the direction of arrow “A” atminimal additional cost and weight.

Referring now to FIG. 22 and FIG. 23 of the drawings, in one embodimentthe present invention provides a reinforced bumper 200 for a motorvehicle. The design of bumper 200 is similar to that of door beam 100(of FIG. 15) in some respects. Accordingly, outer bumper shell 202 isprovided which is in the nature of a C-section having flange portions204. Located in the midspan of shell 202 preferably the centralone-third portion (and preferably at least more than about the middleone-eighth of said shell 202), reinforcement 206 is shown having a layerof structural foam 208 disposed between the inner surface of bumpershell 202 and thin, ultra high-strength inner shell 210. Bumper shell202 will typically be formed of steel (mild steel or non-heat treatedhigh-strength steel) having a thickness of from about 0.050 to 0.080inches. Foam layer 208 will be one of the preferred resin-basedthermally expanded materials previously described and will have athickness of from about 0.060 to about 0.25 inches. Inner shell 210 willhave a thickness of from about 0.030 to about 0.080 inches and will bemade from high-strength steel.

As with the reinforced door beam previously described, the thermallyexpandable resin layer may be extruded, cut to length, and placed oninner shell 210 as a carrier. It may then be inserted in place in bumpershell 202. Preferably after assembly of the vehicle, the resin isthermally expanded to form a light weight foam layer having ahigh-strength inner shell.

It will be appreciated, then, that the side impact beams and bumpersshown in FIGS. 15-23 derive unexpected cost savings and quality by (1)using mild steel or non-heat treated steel as the outer shell (which hasthe greatest mass) and only a small amount of high-strength steel as thelocalized inner shell and (2) by minimizing the amount of resin which isused. It will be understood that the mild strength steel holds itsgeometric shape after forming (does not exhibit spring back) much betterthan heat treated steel.

While the invention has been described primarily in connection withautomotive or vehicle parts, it is to be understood that the inventionmay be practiced as part of other products, such as aircrafts, ships,bicycles or virtually anything that requires energy for movement.Similarly, the invention may be used with stationary or staticstructures, such as buildings, to provide a rigid support when subjectedto vibration such as from an earthquake or simply to provide alightweight support for structures subjected to loads. Additionally,while the invention has been described primarily with respect to heatexpandable foams and with respect to metal parts such as the inner tubes16, 58 and 76, other materials can be used. For example, the foam couldbe any suitable known expandable foam which is chemically activated intoexpansion and forms a rigid structural foam. The support member, such asthe inner tube, could be made of materials other than metal such asvarious plastics or polymeric materials or various wood type fibrousmaterials having sufficient rigidity to function as a back drop orsupport for the foam. Where a heat expandable foam is used the supportor backdrop should be able to withstand the heat encountered during theheat curing. Where other types of foam materials are used, however, itis not necessary that the support member be able to withstand hightemperatures. Instead, the basic requirement for the support member isthat it have sufficient rigidity to function in its intended manner. Itis also possible, for example, to use as the support member materialswhich in themselves become rigid upon curing or further treatment. Theinvention may also be practiced where the outer member or beam is madeof materials other than metal. It is preferred, however, that materialsbe selected for the substrate and backdrop as well as the foam so thatthe thin unexpanded foam upon expansion forms a strong bond with thesubstrate and backdrop so that a structural composition will result.Further, the invention may be practiced where, instead of a beam asdescribed, other constructions with the support or backdrop may also beused.

In a broad sense, the invention in one aspect may be considered asproviding the expandable foam with a support or backdrop in the form ofa tube, foil or other form including a solid or rigid foam. Where asolid or rigid foam is used as the support or backdrop, the foam supportis preshaped in sheets and expanded either by heat or chemically withthe specific practice of the invention representing a balance betweenperformance and weight tradeoff.

What is claimed is:
 1. A laminate support beam comprising an elongatedlongitudinal outer structural member having an outer wall surface and aninner wall surface, portions of said inner wall surface being spacedfrom each other defining a channel therebetween; and a longitudinalrigid inner member having an outer wall surface and an inner wallsurface, said outer wall surface of said inner member generallyconforming in shape to said channel of said outer structural member andbeing slightly smaller in size whereby there is a gap between said outerwall surface of said inner member and said inner wall surface of saidouter member; said outer wall surface of said inner member beingprecoated with a structural foam layer having a thickness of about 0.060to about 0.50 inches, said foam being bonded to said outer wall surfaceof said inner member; said inner member and said structural foamcomprising a drop-in insert unit for said channel to form a multilayerlaminate having a layer of shape-retaining structural foam spread oversaid outer surface of said inner member whereby said foam is generallyshape-retaining before said laminate is dropped into said channel withsaid layer of structural foam thereby disposed toward said inner surfaceof said outer member after said laminate is dropped into said channel;said structural foam being heat expandable whereby upon by applicationof heat and curing of said foam said foam is capable of filling said gapto intimately bond to said inner surface of said outer member and toprovide a lightweight reinforcement for said outer structural member,said foam comprising from 35 to 95% by weight of a synthetic resin and1-60% by weight of a cell forming agent and 1-55% by weight of a filler,and said foam having a density of about 15-40 pounds per cubic foot. 2.The beam of claim 1 wherein said channel has an open top, and said outerstructural member is made of metal.
 3. The beam of claim 1 wherein saidouter structural member is a door beam shell having spaced first andsecond ends and a length therebetween, and said inner member of saiddrop-in insert unit is disposed approximately midway between said firstand second ends and occupies less than about ⅓ the length of said doorbeam shell.
 4. The beam of claim 3 wherein said door beam shell has apair of lateral flanges extending outwardly from said channel atapproximately 90° to said outer wall surface of said door beam shell,and said inner member has a pair of lateral flanges secured to saidflanges of said door beam shell.
 5. The beam of claim 1 wherein saidouter structural member is made of high strength steel.
 6. The beam ofclaim 5 wherein said high strength steel has a thickness no greater thanabout 0.10 inches.
 7. The beam of claim 1 wherein said outer structuralmember is a bumper shell having spaced first and second ends, said innermember of said drop-in insert unit having a length which is less thanabout ⅓ of a length of said bumper shell, and said inner member islocated approximately midway between said first and second ends of saidbumper shell.
 8. The beam of claim 1 wherein said structural foam layerhas a thickness of from about 0.060 to about 0.25 inches.
 9. The beam ofclaim 1 wherein said inner member has a thickness of from about 0.030 toabout 0.080 inches.
 10. The beam of claim 1 wherein said outerstructural member is a radiator support beam, said channel has an opentop, and said open top is closed by a cap attached directly across saidchannel.
 11. The beam of claim 1 wherein said structural member is arocker panel assembly, said rocker panel assembly has an inner panel andan outer panel secured together to form a closed combined panel, andsaid inner member of said drop-in insert unit is disposed within saidclosed combined panel.
 12. The beam of claim 1 wherein said structuralmember is a windshield pillar comprising a pillar outer member havingsaid channel, said drop-in insert unit being in said channel, and saidchannel is closed by a further pillar member.
 13. The beam of claim 1wherein said outer structural member is a drive shaft of generallycircular crosssection, and said inner member of said drop-in unit is ofgenerally circular cross section.
 14. The beam of claim 1 wherein saidstructural member is a C-rail having a pair of side walls and anintermediate connecting wall and being open at said side walls oppositesaid intermediate connecting wall, and said inner member is of a shapeconforming to a shape of said C-rail.